MONDAY, JUNE 7 (Health.com) — If you want to know what's in your TV dinner or Twinkies—a big if—all you need to do is look on the package. But if you smoke cigarettes and want to know what you're inhaling, you're out of luck.

For years, tobacco companies have been lacing cigarettes with hundreds of chemicals and additives ranging from ammonia to cocoa, reportedly to heighten the kick of nicotine, improve flavor, and mask the harshness of smoke. Very little is known about the health effects of these ingredients, however, since the tobacco industry isn't required to disclose them publicly or explain their purpose.

The mystery may soon come to an end. On Tuesday, a Food and Drug Administration (FDA) advisory panel will meet to investigate what "harmful or potentially harmful" ingredients are in the more than 300 billion cigarettes smoked in the U.S. each year. After a second meeting this summer, the panel will provide a list of ingredients and recommendations to the FDA, which was granted the authority by Congress to regulate tobacco products in 2009.

"Maybe with a new FDA ruling, companies will have to tell us what they put in these products and why," says Norman Edelman, MD, the chief medical officer of the American Lung Association. "The concern is that these [ingredients] have health risks and we don't really know what they are."

Sixty years ago cigarettes contained few additives. But as tobacco companies sought to reduce the levels of nicotine and "tar" in cigarettes in response to mounting health concerns, they turned to additives to compensate for the loss of flavor and kick. By the 1990s, additives comprised as much as 10% of a cigarette's weight, according to industry documents that have been made public as a result of tobacco litigation.

Although the recipe of additives in specific cigarette brands remains a heavily guarded industry secret, scientific research, industry documents, and voluntary (though sketchy) disclosure by tobacco companies have shed some light on cigarette ingredients as a whole.

Some of the additives—such as sugar, cocoa, and licorice—sound harmless, even tasty. Others sound lethal. Ammonia (a chemical found in household cleaners), butane (a flammable gas often used as lighter fluid), acetone (the main ingredient in nail polish remover), and nitrate (a component of fertilizers) have all been identified as cigarette ingredients.

Experts say these chemicals and flavors make cigarettes easier to light and burn, smooth out tobacco smoke, and help the body absorb nicotine more readily—all of which could potentially make cigarettes more addictive and harmful.

"We know that cigarettes are not just tobacco rolled in paper," says Danny McGoldrick, vice president of research at the Campaign for Tobacco-Free Kids, an antismoking advocacy group based in Washington, D.C. "They're highly engineered drug-delivery devices."

The effects of some ingredients are better understood than others. Perhaps the most researched tobacco additive is ammonia, which occurs naturally in tobacco in very small amounts and has been added to cigarettes since the 1950s.

Ammonia is believed to enhance the flavor of cigarettes, but it also increases the amount of nicotine that smokers absorb into their bodies, says James Pirkle, MD, deputy director for science at the National Center for Environmental Health, a division of the Centers for Disease Control and Prevention (CDC).

"Ammonia is a base," Dr. Pirkle explains. "When you add that … the nicotine goes to a more basic form which is more volatile, so it comes off [the tobacco] easier. Adding ammonia or any base to a cigarette makes the nicotine generally more available."

The task of the FDA panel—to determine which tobacco ingredients (or "constituents") pose a health risk—is more complicated than it may seem, partly because the many ingredients in cigarettes interact with each other and may be altered when the tobacco is burned. (The panel will compile a separate list of the constituents in tobacco smoke, in fact.)

Even seemingly innocuous additives such as cocoa could prove to be harmful in a burning cigarette, McGoldrick says. "Cocoa might be fine, but when you light it on fire and breathe it into your lungs, it's a different story," he says.

The industry, meanwhile, has argued that additives don't pose health risks above and beyond those associated with smoking in general. A report commissioned by the industry in 1994 stated that 98% of the ingredients added to tobacco are considered safe by the FDA, and many are approved as food additives.

"We want to make sure that nothing is added to cigarettes that affects the addictiveness or toxicity of the product," Dr. Pirkle says. Although the CDC is actively researching the components of tobacco, he adds, "Regulation falls with the FDA."

The disclosure and regulation of tobacco ingredients has been a long-standing—and long-thwarted—goal of public health officials and legislators.

The federal government has had lists of cigarette ingredients for years, but it hasn't been able to publicize the lists or restrict the use of additives. Federal law has required tobacco companies to submit a list of ingredients in their cigarettes to the U.S. Department of Health and Human Services each year since 1986, but those lists are confidential because they're considered trade secrets.

Now, for the first time, the FDA has the authority to regulate cigarette ingredients.

While Dr. Edelman is glad that the FDA is taking action, he says that the ultimate goal of any policy stemming from the panel's findings should be to eliminate smoking rather than reduce its health risks.

"If the idea is to make a safer cigarette, I don't like it," he says. "Tinkering with the additives, maybe you'll have a few less carcinogens. The only way to be safe from cigarette smoke is to not be exposed to cigarette smoke."

McGoldrick agrees that there's no such thing as a safe cigarette. But he adds that identifying and phasing out harmful additives could save lives. "If we could make a cigarette that was half as harmful as they are now for [smokers] who are unable to quit, it might be a good thing to do," he says.